1. (Field of the Invention)
The present invention relates to a combustion engine of a vertical shaft type having a vertically extending crankshaft, which engine may be employed for driving a working machine such as a lawn mower.
2. (Description of the Prior Art)
The conventional combustion engine of a vertical shaft type includes an engine body made up of a crankcase, in which a crankshaft is supported to extend vertically, and an engine cylinder block integrated together with the crankcase and accommodating a horizontally laid reciprocating piston, which is in turn drivingly connected to the crankshaft through a connecting rod. The engine body of the conventional combustion engine has a lower end face, with which a mount base serving to define both an oil pan of the engine and the mounting of a working machine such as a lawn mower is connected through a gasket. See, for example, the Japanese Utility Model Registration No. 2505523. The conventional combustion engine is mounted on an upper surface of the working machine, with an output shaft extending from a lower end of the crankshaft and connected to a driven unit of the working machine.
In the conventional vertical shaft type combustion engine, the plane of joint between the engine body and the mount base is positioned proximate to the oil pan positioned at a lower portion of the combustion engine. This structural feature poses the following problems: Specifically, in the conventional combustion engine, the surface level of an oil contained within the oil pan lies proximate to the plane of joint between the engine body and the mount base. Accordingly, sealing is required to avoid an undesirable leakage of the oil within the oil pan to the outside through the plane of joint, which would otherwise occur under the influence of vibrations of the combustion engine during the operation and when vibrations occurring in the working machine then connected with the combustion engine are transmitted to the engine body through the mount base.
Also, in the conventional combustion engine, since the extra mount base intervenes between the engine body and the working machine, securing of sufficient mounting rigidity for mounting the combustion engine firmly on the working machine has to be considered.
As an additional problem inherent in the conventional combustion engine, the thermal conduction from the oil pan to the cylinder block and the crankcase tends to be hampered by the presence of the gasket at the plane of joint and, therefore, the effect of cooling the oil pan through the cylinder block and the crankcase, both of which are air cooled, is so low that the temperature of the oil may not be lowered as desired. Also, during the servicing of the combustion engine, the working machine is required to be separated from the combustion engine, followed by removal of the mount base from the engine body, and, accordingly, it is indeed troublesome and time-consuming to accomplish the servicing of the combustion engine.
Furthermore, since the conventional combustion engine is so designed that a cam gear is meshed with a crank gear positioned proximate to the surface level of the oil within the oil pan and is in turn meshed with a governor gear of a governor mechanism, a governor shaft carrying the governor gear is rotatably received in a mounting hole defined in a portion of a side wall of the cylinder block adjacent the surface level of the oil within the oil pan. Because of this structural feature, sealing is required to avoid leakage of the oil to the outside through the mounting hole proximate to the oil surface level during the operation of the combustion engine.
Also, since a part of the governor gear is positioned to be immersed in the oil within the oil pan, the oil is stirred up, resulting in increase of the oil temperature. Yet, since in the conventional combustion engine a gas-oil separating chamber of a breather passage, through which blow-by gases flows from a combustion chamber of the combustion engine, is arranged at a location adjacent a portion of a cylinder head distant from an intermediate portion of the engine cylinder block, that is, at a location laterally of the entire engine structure, the separated oil remaining within the gas-oil separating chamber may leak into an intake passage through the breather passage when the combustion engine is tilted with the cylinder head oriented downwards.